After seeing the list of your fish, the advice of the store you went to becomes even worse. If it were me, I'd never do business with them again
. As well as visiting the board (a good start to getting advice from experienced people not selling you anything), I'd suggest reading some books and getting involved with your local hobbyists.
Brad has given some good advice. If you're experiencing aggression between the yellow tangs (a common problem), your best bet would be to remove the most aggressive and fine a new home for it. Repeat as neccessary and you may just end up with one. Tangs of the same genus often don't tolerate one another.
Oh yeah, Welcome to the board
